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uk Health & medical scares sudden flank pain • pain in side of back • pain comes in waves • can’t get comfortable • cramping side pain • severe one-sided back pain • pain radiating to groin • nausea with flank pain • vomiting with side pain • possible kidney stone pain • possible renal colic • blood in urine concern • pain with peeing • fever with back pain • shivering with pain • can’t pass urine • urgent same-day assessment • sudden abdominal side pain • one-sided lower rib pain • sudden loin pain

What to do if…
you develop sudden flank pain that comes in waves and makes it hard to get comfortable

By PanicStation.org Reviewed under our editorial policy Last reviewed: UK guide

Short answer

Get urgent same-day medical advice: contact NHS 111 (or your GP) now, and go to A&E immediately if the pain is severe/uncontrolled, you have fever/shivering, you cannot pass urine, or you’re vomiting repeatedly.

Do not do these things

  • Do not “wait it out” if you have fever/feel hot and shivery, worsening pain, persistent vomiting, or you cannot pass urine.
  • Do not exceed the label dose of any pain medicine. Do not take two anti-inflammatories (NSAIDs) together (for example ibuprofen plus naproxen). If you’re unsure what’s safe for you, ask NHS 111 or a pharmacist.
  • Do not drink alcohol or take recreational drugs to cope — they can worsen dehydration and make assessment harder.
  • Do not drive yourself to get help if you feel faint, drowsy, or are in distracting pain — ask someone to take you or call 999 if you can’t travel safely.
  • Do not ignore new blood in your urine, burning when peeing, or feeling generally unwell — these can change how urgently you need to be seen.

What to do now

  1. Do a 60-second safety check. If you have any of the following, go to A&E now or call 999 if you can’t get there safely:
    • pain that is severe or not settling with simple measures
    • a high temperature, or you feel hot, cold, sweaty, or shivery
    • you are unable to pass urine (or you’re passing very little)
    • repeated vomiting so you can’t keep fluids down
    • you are pregnant, immunocompromised, have a single kidney, or significant kidney disease
  2. If you don’t have the red flags above, but the pain is still wave-like and hard to sit still with: contact NHS 111 for urgent same-day advice (or your GP if they can see you urgently). Say: “sudden flank/loin pain in waves, can’t get comfortable,” and mention any nausea/vomiting, urinary symptoms, pregnancy possibility, or kidney history.
  3. Write down three details for triage (it speeds things up):
    • your temperature (if you can check it)
    • when you last passed urine and whether it was painful or bloody
    • what pain relief you’ve taken (name + time)
  4. Use safer comfort measures while you arrange care.
    • If you can take them safely, use over-the-counter pain relief exactly as directed on the packet (avoid anything you’re allergic to or have been told not to take).
    • A warm bath or heat pack on the sore side can help some people. Stop if it makes you feel worse or light-headed.
  5. Prepare to be assessed. If you’re going to urgent care/A&E:
    • bring a list of medicines, allergies, and key conditions
    • be ready to provide a urine sample
    • arrange transport (pain can spike suddenly)

What can wait

  • You do not need to decide right now what the cause is (kidney stones are one possibility, but not the only one).
  • You do not need to force large amounts of fluid during severe pain or active vomiting.
  • You do not need to plan follow-up tests or long-term prevention today; first priority is ruling out infection/obstruction and getting pain controlled.

Important reassurance

Wave-like flank/loin pain that makes you restless and unable to get comfortable is a common reason for urgent assessment. Getting checked promptly is a sensible, protective step — especially because infection with blockage needs fast treatment.

Scope note

This is first-steps-only guidance for the next few hours. Further decisions (tests, imaging, antibiotics, procedures, prevention) depend on what clinicians find.

Important note

This is general information, not a diagnosis. If you are worried, symptoms are severe, or you have fever/shivering, persistent vomiting, or trouble passing urine, seek urgent medical care immediately.

Additional Resources

About this guide

PanicStation.org guides are written as plain-English first steps, then reviewed for clarity, jurisdiction, and source quality. If you notice an error, outdated information, unclear wording, or a broken link, please contact us.

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